Iruka - sensei would be a great character to include. He could be the one who tries to stop the others from making fun of Naruto, or he could be the one who gently explains to Naruto why his actions are causing the others to laugh. Kakashi might also be in the story. He would probably just watch with his lazy eye and make some dry comments about the whole situation, adding to Naruto's confusion.
Sasuke could be involved. He might be one of the ones making fun of Naruto, in his typical aloof way. Or he could be in the background, just observing and secretly finding it a bit funny while pretending not to care. Sakura could also be there. She might scold the others for making fun of Naruto, or she could join in the teasing a little bit out of her own insecurities.
Sakura could be involved. She could be like a healer or an advisor in the new world. Her medical skills would be very useful. Also, Sasuke might be there. He could be a sort of enforcer, using his Sharingan to detect threats. In the world of Asgore, they could form a new kind of team, with Naruto as the leader like Asgore. And then there could be characters from Asgore's world like Toriel. She could be a guide to Naruto about the culture and history of the place.
Hinata would also be very involved. She has deep feelings for Naruto. She might be at his bedside in the hospital, praying for his recovery. After his death, she would be heartbroken and might have to find a new purpose in life without Naruto.
One possible plot could be that Naruto is made fun of during a Christmas party in the Hidden Leaf Village. Maybe because he doesn't understand some of the Christmas traditions that the villagers have adopted from other cultures. For example, he might get confused about gift - giving and end up giving something really strange, and the other villagers make fun of his naivete.
Sasuke could be involved. He might either try to stop Naruto from leaving, believing that they should face whatever comes together in Konoha, or he could decide to join Naruto on his journey, as they have a deep bond.
In addition to Naruto and Pakura, Hinata could be involved. She has a crush on Naruto, and with him being adopted by Pakura, she might be shy yet eager to interact with him in this new context. Rock Lee could also be in the story. He is always looking for strong opponents and new training methods. Naruto's new situation under Pakura's care might intrigue him, and he could try to learn from Naruto's new experiences. And of course, Orochimaru might be interested in Naruto's adoption as well, seeing it as a way to potentially get closer to Naruto for his own devious plans.
Sasuke could be involved. He might be initially against Naruto's plan to capture Lemon, thinking it's a waste of time. But later, he realizes the importance and joins Naruto. Sakura could also be there. She might use her medical ninjutsu to help Naruto if he gets injured during the capture process. Kakashi could be a guiding figure, providing Naruto with strategic advice on how to approach Lemon.
Sasuke could be involved. Since they have a complex relationship, Sasuke might either be a rival during Naruto's training, pushing him to be better, or he could end up joining Naruto in some training sessions to become stronger together.
Sasuke is an obvious choice. He has a connection to Naruto that goes beyond just friendship or rivalry. He might be the one who first discovers Naruto's predicament and sets out to find a solution. Sakura is essential too. Her skills as a medical ninja are crucial. She could be the one who patches Naruto up every time he gets injured in his fight against whatever is threatening his life. Also, characters like Jiraiya might make an appearance. Even though he's dead in the original story, in this fanfiction, he could come back as a spirit guide to help Naruto find a way to 'refuse to die', giving him advice based on his own knowledge and experiences.
Sasuke is likely to be involved. He and Naruto have a complex relationship and Sasuke has become an ally. He could offer his strength in combat to protect the rebuilding efforts. Also, Sakura. She's a skilled ninja with medical abilities that could be useful if there are any injuries during the process.
There might be characters from Iwa who oppose Naruto. For example, the Tsuchikage of Iwa would surely be involved as the leader of the village Naruto is attacking.